The Mechanisms of Decay and Decomposition

Lance Pearson

Number of Learners: 90 Students

Date: 03/04/05

Grade (or Age): 8th grade

School/Town: Timilty Middle/Roxbury

Estimated Length of Session: 60-80 minutes

Curriculum Area: Science (Biology)

PREREQUISITE KNOWLEDGE AND SKILLS

Students have an understanding that all living things die, with many likely having lost a pet or even a relative. From previous class work, students have been introduced to the life cycle and the concept of an ecosystem which is part of nearly every middle school science curriculum. As a result, students have at least an introductory exposure to trophic levels (producer-consumer-decomposer) in the environment.

CONTENT TO BE TAUGHT

This lesson plan centers upon scientific observation of the decay and decomposition process of (previously) living things (plants: apple; animals: meat) in a manner that is largely student-directed. Through this lesson plan students will be gain increased familiarity with some common decomposers and scavengers (bacteria, flies) in an urban environment and their role in the larger ecosystem.

RATIONALE

Unlike the growth of producers or consumers which are invariably integral parts of the science curriculum, students in urban school settings are rarely asked to deeply examine the processes of decay and decomposition. This guided-inquiry lesson plan rounds out the standard life cycle curriculum with in-depth scientific observations of the mechanisms of decomposition and decay. In so doing, it fulfills one of the more neglected Massachusetts Frameworks Life Science (Biology), Grades 6–8 curriculum standards: 15. Explain how dead plants and animals are broken down by other living organisms and how this process contributes to the system as a whole.

An additional rationale for implementing this curriculum is that it fits seamlessly as a supplement to the existing FOSS Populations & Ecosystems curriculum, paralleling the existing terrarium project in both timing and design. As such, it can be added with a minimum of additional class and teaching time.

GOALS

  • Students will collaborate amongst themselves (jigsaw) to explore some of the principle decomposers in the urban environment.
  • Students will design an experiment to monitor the decomposition of a plant and an animal.
  • Students will engage in self-generated data observation to (a) hone their scientific writing and observational skills and (b) form conclusions about the processes of decomposition.
    •

    PERFORMANCE OBJECTIVES

  • Students will observe some of the principal decomposers in an urban environment by designing an experiment to record decay over the course of weeks of a plant and an animal under differing conditions.
  • Each student will be responsible for proposing an experimental protocol related to the way in which plants and animals decompose including: a) an experimental question, b) an experimental hypothesis, c) a list of materials, d) an experimental design consisting of at least 5 different steps, and e) a sample data sheet.
  • Each student will be required to design a data sheet and make detailed and regular observations (during the first 5 minutes of every class for two weeks) of the class' science experiment. Students will be monitored and graded upon relevance, detail and accuracy of their selected data.
    •

    MATERIALS

  • Enclosed aquarium
  • Panels to subdivide aquarium into compartments (plastic or card board)
  • Piece of fruit (sliced, e.g. Apple; students can decide as a group if desired) and/or slice of bread
  • Package of meat (without preservatives, e.g. Turkey; students can decide as a group if desired)
  • House flies (several)
  • Air freshener
    •

    Optional
  • Anything else your students might want to watch decompose (for instance, the McDonald's Fries)
  • Earthworms
  • Soil
  • Rubbing (Isopropyl) Alcohol
    •

    PROCEDURE

    This curriculum works best when performed in conjunction with the terrarium observations which form an early portion of the current Populations & Ecosystems curriculum. Ideally, you would start this project approximately one week after the terrarium has been set up and students have begun making those observations.

    A. Opener
  • Begin with an open-response question session probing student understanding of the life cycle and trophic levels (which they have been exposed to in 7th grade and have been reviewing previously in the Populations and Ecosystems curriculum). Example questions: What are some examples of Producers (Consumers)? What is the role of Producers (Consumers in the life cycle)? What happens when a living thing dies (give examples like a cat or a flower)?
    •
  • Begin to focus questioning on specifics of decomposers to be covered: What are some examples of decomposers and scavengers in the environment? What are some examples of things that eat dead animals? What are the decomposers in the terrarium we set up…?
    •

    B. Development
  • Present information sheets (Give one decomposer to each person, Appendices) and ask students to read about some of the principle consumers in the urban environment.
  • Have the students jigsaw (share what they read) with surrounding students that have differing decomposers to get a more complete picture of the range of decomposers in the urban environment.
  • A student presentation of these decomposers to the class is a good extension.
  • Present basic materials list for students to use in designing a hypothetical experiment: materials section.
  • Ask students to design an experiment (gauge how detailed this should be based upon class level and previous experience) to explore the way some common decomposers like flies and bacteria affect living things for homework (class time can be dedicated to this if teacher assistance is deemed necessary). Ideally, this would include: an experimental question and hypothesis, a list of materials, an experimental design consisting of at least 5 different steps and, a sample data sheet.
  • Next set-up class experiment. Place dividers in aquarium marking off at least 3 different compartments. In each compartment place a piece of meat and a piece of sliced fruit (and/or piece of bread) put through a separate experimental condition. Different conditions include: (a) flies present, (b) bacteria-laden matter (handled extensively with hands), and (c) a control condition (if desired, place in rubbing alcohol before then placing them in compartment).  You want to make sure the items stay very moist (perhaps spraying with de-ionized water several times everyday; or even placing them in separate very shallow pools of water) because a hot, dry environment (like a normal classroom) will cause the items to dehydrate which stops bacteria from growing. Additional conditions can be student generated, for instance, bury the items in soil with earthworms.
    •

    C. Closing
  • Have each student devise a data sheet for this experiment.
  • Have students collect data at the start of class every day for 2-3 weeks (or as long as desired), in conjunction with their terrarium observations.
  • Debrief students on their observations either as a guided discussion or in the form of individual written responses. Example questions: What is the role of decomposers? Decomposers are organisms that break down non-living organic matter by feeding on it. Which conditions resulted in faster decomposition of the materials? Those with more bacteria. How did the decomposition process of the animal and plant differ? White mold grew on the plants and started earlier than decay appears on the animal. How did the flies affect decay? Decay was much faster.
    •

    ACCOMMODATIONS

    Establishing a word wall with key words and definitions like decompose, decomposers, fly, maggot, bacteria, larvae can be a great assistance to English-learners. Also, consultation with these students during their daily data recording could be very beneficial.

    EVALUATION

    The quality of the students' experimental protocol proposals allows for insight into student understanding of both the initial decomposer information jigsaw and scientific reasoning. If more focused evaluation of this initial information is desired, teacher-led discussion of the data is a clear possibility.

    Each student will be required to design a data sheet for the class experiment and make detailed and regular observations (first 5-10 minutes of every class for two weeks or more). Monitoring these data sheets regularly allows the teacher to pinpoint comprehension or execution difficulties. The ability of students to propose novel experimental conditions for the class experimental project is an indication of student interest and creative scientific thinking about the new content. Additionally, debriefing of students after the experimental observations allows for assessment of student comprehension.

    EXTENSION

    Additional material for student individual exploration or exploration as a class, including time-lapse videos of decomposition of animals, can be found at any of the sites in the reference section (especially the last two). If access to digital camera equipment is possible, time-lapse observation can be conducted on the experiment in the lesson plan, as well.

    REFERENCES

    Forensic Entomology:

    http://www.ndsu.nodak.edu/entomology/topics/forensic.htm

     

    Additional information about Fungi:

    http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0010851.html

     

    Additional information on the role fly larvae (maggots) play in decomposition:

    http://deathonline.net/decomposition/corpse_fauna/flies/maggots.htm

     

    Additional information on bacteria and the role they play in decomposition:

    http://deathonline.net/decomposition/corpse_fauna/bacteria.htm

    http://www.microbe.org/microbes/bacterium1.asp

     

    Additional information on rats:

    http://www.nsrl.ttu.edu/tmot1/rattnorv.htm

    http://www.bbc.co.uk/nature/wildfacts/factfiles/273.shtml

     

    Additional information on beetles:

    http://www.deathonline.net/decomposition/corpse_fauna/beetles/index.htm

     

    Additional information about moths:

    http://www.deathonline.net/decomposition/corpse_fauna/moths.htm

     

    ASSOCIATED APPENDICES

    Appendices for Decomposers Lesson Plan